The scale on a map is 6cm : 8km. If the distance between two cities is 56km, how far apart in cm are the two cities on the map?
Explanation: The scale means that every 6cm on the map corresponds to an actual distance of 8km. An actual distance of 56km is the same as 7 $\cdot$ 8km. The distance between the two cities on the map is 7 $\cdot$ 6cm, or 42cm.